Combination filter for filtering fluids

ABSTRACT

The present invention provides a combination filter for filtering fluids comprising a flow channel particulate filtration media having a first face and a second face and a gas adsorbing filtration media. The flow channel particulate filtration media comprises a plurality of flow channels directed in flow direction and defined by inner surfaces. The flow channels having inlet openings through the first face and outlet openings through the second face of the flow channel particulate filtration media. The inner surfaces of said flow channels at least in part are provided with structures protruding therefrom and forming or extending into the flow channels or an electrical charge or a combination of both. The said gas adsorbing filtration media comprises a pad having a first face and a second face and width and length dimensions orthogonal with respect to each other and each individually to the flow direction and having a thickness dimension in flow direction. The pad comprising a layer extending substantially perpendicular to the flow direction across the width and length dimensions of the pad.

TECHNICAL FIELD

The present invention relates to a combination filter system forfiltering fluids, particularly gases, particularly for filtering airstreaming into the passenger cabin of a vehicle.

BACKGROUND OF THE INVENTION

Combination filter systems for filtering air streaming into thepassenger cabin of a vehicle are known. Such filter systems typicallycomprise a particulate filter media with a sorbent filter media.

For example, WO-A-95/26802 discloses a combination filter system whichcomprises a pleated electret charged fiber/nonwoven filter media and anactive carbon particle pad. Although the active carbon particle padexhibits good gas efficiency and/or gas capacity depending on thethickness and carbon content of the pad, the application of such anactive carbon particle pad causes a high pressure drop. A high pressuredrop is undesirable for vehicle cabin filter systems.

EP-A-383236 discloses an adsorber particle layer that is co-pleated withan electret charged fiber non-woven layer. Although such a combinationfilter has an acceptable pressure drop, the lifetime thereof is limited,i.e. the filter needs to be replaced frequently.

It is therefore desirable to further improve combination filters, inparticular to increase the lifetime of such a filter without raising thepressure drop of such filter to an unacceptable level. Also, for use inmotor vehicles, the filter should preferably be designed to meet safetyregulations existing in the automotive industry. Further, thecombination filter should preferably have the same or improved filterperformance. It is furthermore preferred that the combination filter canbe produced in a cost effective and easy way and can be easily andeffectively installed in a motor vehicle for the purpose of filteringgaseous fluids entering the passenger cabin of such motor vehicle.

SUMMARY OF THE INVENTION

The present invention provides a combination filter for filtering fluidsflowing in a flow direction, comprising

-   -   a flow channel particulate filtration media having a first face        and a second face and    -   a gas adsorbing filtration media,    -   wherein said flow channel particulate filtration media comprises        a plurality of flow channels directed in flow direction and        defined by inner surfaces, said flow channels having inlet        openings through the first face and outlet openings through the        second face of said flow channel particulate filtration media,    -   wherein the inner surfaces of said flow channels at least in        part are provided with        -   structures protruding therefrom and forming the flow            channels or extending into the flow channels or        -   an electrical charge or        -   a combination of both and    -   wherein said gas adsorbing filtration media comprises a pad        having a first face and a second face and width and length        dimensions orthogonal to both each other and the flow direction        and having a thickness dimension in flow direction, said pad        having at least one portion of substantial constant thickness        said portion extending over the width and length dimensions of        said pad.

The combination filters according to the invention exhibit anadvantageously low pressure drop over its lifetime. In other words thecombination filters according to the invention show a relatively flatincrease in pressure drop with loading over the lifetime of the filter,and hence, a corresponding long lifetime and high capacity.

The particulate filtration media of the present combination filter is aflow channel particulate filtration media having a relatively lowincrease in pressure drop with loading over the lifetime of the filter.Surprisingly, this advantage is still given if the flow channelparticulate filtration media is combined with a gas adsorbing filtrationmedia having the form of a pad which is substantially flat or even. Thepad comprises a layer extending substantially perpendicular to the flowdirection across the width and length dimensions of the pad. The layerhas a thickness which may be substantially constant along the width andlength dimensions of the pad. As an alternative, the layer comprisesportions of different thicknesses in that the first or second face orboth faces of the pad, e.g. is or are structured in particularcorrugated, so as to increase the surface area subjected to the fluidflow cross section. The faces of the pad preferably are parallel to eachother and in particular also parallel to the first and second faces ofthe flow channel particulate filtration media. Accordingly, the gasadsorbing filtration media of the combination filter according to theinvention does not have a pleated structure but may have first andsecond opposite faces at least one of which is provided with structures(e.g. protrusions and recesses) in order to increase the surface areaaffected by the fluid to be filtered.

In particular, according to a preferred embodiment of the invention, theflow channel particulate filtration media is formed by at least onestructured film layer and a second layer, the structured film layerhaving a first face and a second face, at least one face of thestructured film layer forming, at least in part, said flow channels andhaving high aspect ratio structures over at least a portion of the faceforming said flow channels and wherein a second film layer comprisingthe flow channel layer, or a further layer, at least in part definesordered fluid pathways through the flow channel particulate filtrationmedia and wherein the film layers are preferably electrostaticallycharged and define a plurality of inlets open through the first face anda plurality of outlets open through the second face of said flow channelparticulate filtration media.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a first structured film useful in forming theflow channel particulate filtration media.

FIG. 2 is a side view of a second structured film useful in forming theflow channel particulate filtration media.

FIG. 3 is a side view of a third structured film useful in forming theflow channel particulate filtration media.

FIG. 4 is a side view of a fourth structured film useful in forming theflow channel particulate filtration media.

FIG. 5 is a perspective view of a contoured film and flat cap film layerassembly.

FIG. 5A is a perspective view of a contoured film and flat cap filmlayer assembly with an additional functional layer.

FIG. 6 is a perspective view of a first embodiment of a flow channelparticulate filtration media formed of the FIG. 5 assembly.

FIG. 7 is a perspective view of a second embodiment of a flow channelparticulate filtration media.

FIG. 8 is a perspective view of a contoured film layer with astabilization layer of strands.

FIG. 9 is a perspective view of a contoured film layer with a flat filmcap layer forming a flow channel assembly.

FIG. 10 is a side view of a third embodiment of the flow channelfiltration medium.

FIG. 11 is a perspective view of a fourth structured film useful informing the flow channel particulate filtration media.

FIG. 12 is a schematic representation of a combination filter accordingto a first embodiment.

FIG. 13 is a schematic representation of a combination filter accordingto a second embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The present invention provides a combination filtration media system forfiltering fluids comprising a flow channel particulate filtration mediaand a gas adsorbing filtration media.

The combination filter of the present invention is particularly suitablefor use in a vehicle, in particular a motor vehicle, for filtering airentering a passenger cabin of such vehicle.

The gas adsorbing filtration media of the combination filter is providedin the form of a pad having width and length dimensions orthogonal toeach other and a thickness dimension substantially parallel to the flowdirection. Accordingly, the pad does not provide a pleated structure.The face confronting the flow channel particulate filtration media issubstantially flat. Flat in this sense means that the face can also beprovided with structures (e.g. protrusions and recesses) in particularin wave shape like form so that the surface area of the pad and,accordingly, the gas adsorbing filtration area is increased. The sameflat structure can also be provided at the other face of the padconfronting the face mentioned above.

Accordingly, the pad of the gas adsorbing filtration media is comprisedof a layer having an average thickness of preferably between 0.5 cm toseveral centimeters and, in particular, to 2 cm or 3 cm and extendingsubstantially in a plane generally perpendicular to the flow direction.The length and width dimensions may vary between 100 mm to 400 mm andpreferably 150 mm to 250 mm.

The adsorber particles of the gas adsorbing filtration media can be anyof the known active adsorber particles capable of removing unwantedsubstances such as unwanted gases or smells from a fluid stream.Adsorber particles for use in this invention include active carbonparticles, synthetic polymer adsorbers, activated resins and zeolites.Generally, the particles will have a size between 0.01 and 2 mm,preferably between 0.05 and 1 mm. The particles may be bonded togetherby a binder. Preferably, the adsorber particles used in this inventionare active carbon particles.

The combination filter will generally have the gas adsorbing filtrationmedia located on the down stream side of the flow channel filtrationmedium, i.e. the fluid to be filtered will first pass through the flowchannel filtration medium and thereafter through the gas adsorbingfiltration media.

The gas adsorbing filtration media can be any kind of material suitablefor gas adsorbing and, in particular, is comprised of entangled fibersloaded with activated carbon particles adhered thereto by means of abinder or the like. As an alternative, the gas adsorbing filtrationmedia comprises agglomerated activated carbon particles adhered to eachother to define a porous structure. This structure can be additionallyprovided with holes or channels extending therethrough from the inletface to the outlet face in order to further reduce the flow resistanceof the porous structure. Finally, also a gas adsorbing filtration mediacan be used in which activated carbon particles are attached to anetting structure built from strands of fibers of polypropylene orsimilar materials or an expanded open cell polyurethane foam. Theindividual strands as well as carbon particles are adhered to thestructure utilizing a binder in particular a resin of the polyurethanegroup.

The flow channel particulate filtration media of the combination filteris comprised preferably of charged contoured films arranged in ahoneycomb structure to form fluid flow pathways. The flow channelparticulate filtration media also comprises film layers where at leastsome of the film layers have high aspect ratio structures such as ribs,stems, fibrils, or other discrete protuberances which extend the surfacearea of at least one face of the film layer.

Film layers are configured in a flow channel particulate filtrationmedia with the contours of the film layers defining a plurality of inletopenings into fluid pathways through a face of the array. The filmlayers may have structures defining the fluid pathways or extendtherein. The fluid pathways may be defined by a single contoured filmlayer having a cap film layer, or by adjacent contoured film layers. Thefluid pathways further have outlet openings which allow fluid to passinto and through the pathways without necessarily passing through afilter layer having a flow resistance. The fluid pathways and openingsof the flow channel particulate filtration media as such are defined byone or more flow channels formed at least in part by the contoured filmlayers. The flow channels are created by peaks or ridges in thecontoured film layer and can be of any suitable form as long as they arearranged to create fluid pathways in conjunction with an adjacent filmlayer through the flow channel particulate filtration media. For examplethe flow channels can be separate discrete channels formed by repeatingridges or interconnected channels formed by peak structures. The flowchannels could also be isolated channels (e.g., closed valleyssurrounded by peaks or ridges) that together with a further contouredfilm layer define a fluid pathway (e.g. where the valleys on theadjacent contoured film layers are offset to create a continuoustortuous path through the filtration media array).

A plurality of adjacent, either separate or interconnected, flowchannels (e.g., a series of flow channels aligned in a row sharing acommon contoured film layer) of the flow channel particulate filtrationmedia are preferably defined by a series of peaks or ridges formed by asingle contoured film layer. These adjacent flow channels define a flowchannel layer. The peaks or ridges in the contoured film layers may bestabilized or separated by a planar or contoured cap layer. A cap layeris a layer which is in engagement, or contact, with the peaks or ridgeson one face of the contoured film layers. The peaks or ridges on theopposite face of the contoured film layer can also be joined to or incontact with a cap layer. A cap layer may cover all or only a portion ofa contoured film layer. If the cap layer is a planar film layer, the capfilm layer and the associated contoured film layer define fluid pathwaysbetween adjacent peaks or ridges of the contoured film layer in contactor engagement with the film cap layer.

A cap layer can also be a functional layer such as a sorbent orparticulate filter or a stabilization layer such as a series ofstabilization filaments or a strengthened nonwoven. FIG. 8 shows acontoured film layer 40 having discrete stemlike structures 46 joined tostabilization filaments 42 at peaks 44 of the contoured film layer 40.In order to be useful as a flow channel particulate filtration media,the FIG. 8 embodiment would need to be joined at a further film layersuch as a cap film layer or a further contoured film layer. If a furthercontoured film layer were joined to the layer of filaments 42, the fluidpathways would be formed from the two flow channel layers of the twoadjacent contoured film layers.

Adjacent flow channels, e.g., 14 and 16, in a flow channel layer 20,defined by a contoured film layer 10, may be all the same as shown inFIG. 5, or may be different as shown in FIG. 9. In FIG. 9, the adjacentflow channels 24 and 26 of the flow channel layer 20 are separate flowchannels, which have the same height but different widths. In FIG. 5 theadjacent flow channels 14 and 16 of the flow channel layer 20 areseparate flow channels which have the same height and widths. Formanufacturability, preferably all, or at least a majority of the peaksor ridges forming the flow channels of the contoured film layer shouldhave substantially the same height. Further, each adjacent flow channellayer 20 of the flow channel particulate filtration media 30 may havethe same flow channel configurations (as shown in FIG. 6), or may bedifferent. The flow channels of adjacent flow channel layers of a flowchannel particulate filtration media may also be aligned (e.g., as inFIG. 6), or may be offset (e.g., at angles with respect to each other asin FIG. 7) or some combination thereof. The adjacent overlying flowchannel layers of a flow channel particulate filtration media aregenerally formed from a single contoured film layer where the flowchannels can be interconnected, separate, or even separate and isolated(i.e. do not extend across the entire contoured film layer). With flowchannels that extend across the entire contoured film layer thesechannels could extend linearly or curved. Preferably, the flow channelsof adjacent overlying flow channel layers are substantially parallel andaligned (FIG. 6), but they could be at diverging or converging angles.If the flow channel particulate filtration media is formed ofcylindrically arranged flow channel layers as shown in FIG. 10, theseflow channel layers can be formed of a single contoured film layer 60with an optional cap layer 62 configured in a corkscrew or helicalalignment around a central axis 64. The contoured film layer ispreferably bonded to one cap layer 62 for stability during manufacturingand in frictional contact with the other cap layers 62 a.

Pairs of contoured film layers may face one another with the facinglayers engaging one another at their respective peaks as shown in FIG. 7or be separated by one or more cap layers as shown in FIGS. 5, 6, and10. When the contoured film layers 31 are in contact without anintervening film layer as shown in FIG. 7, the fluid pathways 33 weavebetween adjacent intersecting flow channels, e.g., 34 and 35 of thecontoured film layers 31.

The flow channels provide controlled and ordered fluid flow pathwaysthrough the flow channel particulate filtration media. The amount ofsurface area available for filtration purposes is determined byavailable surface area of the flow channels and the number and length ofthese flow channels in flow channel particulate filtration media. Inother words, the features of the individual filtration media layers,such as the length of the flow channels, channel configurations, and theface surface area of the individual layers.

A single layer of flow channels provided by a contoured film layer maycomprise a functional flow channel particulate filtration media inaccordance with the present invention, however, preferably multipleoverlying flow channel layers form the functional flow channelparticulate filtration media. A flow channel particulate filtrationmedia formed of stacked contoured structured film layers provides anordered or engineered and mechanically stable porous structure withoutthe pore size variability and gross irregularities of nonwoven filterwebs. Any pore size variability or irregularities are planned andcontrolled based on the ultimate filtration needs for which thecombination filter is intended. As a result, the fluid stream issubjected to uniform treatment as it passes through the flow channels ofthe flow channel particulate filtration media, thus enhancing itsfiltering efficiency. Generally, the contoured film layers forming theflow channels reinforce the flow channel particulate filtration mediaforming a structurally stable form which can be formed into a multitudeof self supporting configurations.

The flow channel particulate filtration media may be conformed into avariety of shapes or laid over objects without crushing and closing theflow channels. The contoured films are electrostaticly charged whilecontoured in association with any attached cap layer or other layer.These layered charged contoured films are characterized by surfacevoltages of at least +/−1.5 KV, preferable at least +/−10 KV, measuredapproximately one centimeter from the film surface by an electrostaticsurface voltmeter (ESVM), such as a model 341 Auto Bi-Polar ESVM,available from Trek Inc., Medina, N.Y. The electrostatic charge maycomprise an electret, which is a piece of dielectric material thatexhibits an electrical charge that persists for extended time periods.Electret chargeable materials include nonpolar polymers such aspolytetrafluoroethylene (PTFE) and polypropylene. Generally, the netcharge on an electret is zero or close to zero and its fields are due tocharge separation and not caused by a net charge. Through the properselection of materials and treatments, an electret can be configuredthat produces an external electrostatic field. Such an electret can beconsidered an electrostatic analog of a permanent magnet.

Several methods are commonly used to charge dielectric materials, any ofwhich may be used to charge a contoured film layer or other layers usedin the flow channel particulate filtration media, including coronadischarge, heating and cooling the material in the presence of a chargedfield, contact electrification, spraying the web with charged particles,and wetting or impinging a surface with water jets or water dropletstreams. In addition, the chargeability of the surface may be enhancedby the use of blended materials or charge enhancing additives. Examplesof charging methods are disclosed in the following patents: U.S. Pat.No. RE 30,782 to van Turnhout et al., U.S. Pat. No. RE 31,285 to vanTurnhout et al., U.S. Pat. No. 5,496,507 to Angadjivand et al., U.S.Pat. No. 5,472,481 to Jones et al., U.S. Pat. No. 4,215,682 to Kubik etal., U.S. Pat. No. 5,057,710 to Nishiura et al. and U.S. Pat. No.4,592,815 to Nakao.

In addition, one or more layers could also have active charging such asby the use of a film, with a metallized surface or layer on one facethat has a high voltage applied to it. This could be accomplished in thepresent invention by the addition of such metallized layer adjacent to acontoured layer, or the application of a metal coating on a layer. Flowchannel filtration medium layers comprising such metallized layers couldthen be mounted in contact with an electrical voltage source resultingin electrical flow through the metallized media layers. Examples ofactive charging are disclosed in U.S. Pat. No. 5,405,434 to Inculet.

Another type of treatment available is the use of fluorochemicaladditives in the form of material additions or material coatings whichcan improve a filter layer's ability to repel oil and water, as well asenhance the ability to filter oily aerosols. Examples of such additivesare found in U.S. Pat. No. 5,472,481 to Jones et al., U.S. Pat. No.5,099,026 to Crater et al., and U.S. Pat. No. 5,025,052 to Crater et al.

Polymers useful in forming a structured film layer used in the presentinvention include but are not limited to polyolefins such aspolyethylene and polyethylene copolymers, polypropylene andpolypropylene copolymers, polyvinylidene difluoride (PVDF), andpolytetrafluoroethylene (PTFE). Other polymeric materials includeacetates, cellulose ethers, polyvinyl alcohols, polysaccharides,polyesters, polyamides, poly(vinyl chloride), polyurethanes, polyureas,polycarbonates, and polystyrene. Structured film layers can be cast fromcurable resin materials such as acrylates or epoxies and cured throughfree radical pathways promoted chemically, by exposure to heat, UV, orelectron beam radiation. Preferably, the structured film layers areformed of polymeric material capable of being charged namely dielectricpolymers and blends such as polyolefins or polystyrenes.

Polymeric materials including polymer blends can be modified throughmelt blending of plasticizing active agents or antimicrobial agents.Surface modification of a filter layer can be accomplished through vapordeposition or covalent grafting of functional moieties using ionizingradiation. Methods and techniques for graft-polymerization of monomersonto polypropylene, for example, by ionizing radiation are disclosed inU.S. Pat. Nos. 4,950,549 and 5,078,925. The polymers may also containadditives that impart various properties into the polymeric structuredlayer.

The contoured film layers and cap film layers may have structuredsurfaces defined on one or both faces. The high aspect ratio structuresused on the contoured film and/or cap film layers of the preferredembodiments generally are structures where the ratio of the height tothe smallest diameter or width is greater than 0.1, preferably greaterthan 0.5 theoretically up to infinity, where the structure has a heightof at least about 20 microns and preferably at least 50 microns. If theheight of the high aspect ratio structure is greater than 2000 micronsthe film can become difficult to handle and it is preferable that theheight of the structures is less than 1000 microns. The height of thestructures is in any case at least about 50 percent or less, of theheight of the flow channels, preferably 20 percent or less. As shown inFIGS. 1–4 and 11 the structures 8 on the film layers 1 can be in theshape of upstanding stems or projections, e.g., pyramids, cube corners,J-hooks, mushroom heads, or the like; continuous or intermittent ridges;e.g., rectangular 3 or v-shaped ridges 2 with intervening channels 5; orcombinations thereof. Mushroom head projections 46 are shown in FIG. 11on film backing 40. These projections can be regular, random orintermittent or be combined with other structures such as ridges. Theridge type structures 8 can be regular, random intermittent, extendparallel to one another, or be at intersecting or nonintersecting anglesand be combined with other structures between the ridges, such as nestedridges 4 or projections. Generally, the high aspect ratio structures 8can extend over all or just a region of a film 1. When present in a filmregion, the structures provide a surface area at least 50 percent higherthan a corresponding planar film, preferably at least 100 percenthigher, generally up to 1000 percent or higher. In a preferredembodiment, the high aspect ratio structures are continuous orintermittent ridges that extend across a substantial portion of thecontoured film layer at an angle to the contours, preferably octagonal(90 degrees) to the contours of the contoured film layer as shown inFIGS. 5 and 6. This reinforces the mechanical stability of the contouredfilm layer in the flow channel assembly (FIG. 5) and the filtrationmedia array (FIG. 6). The ridges generally can be at an angle of fromabout 5 to 175 degrees relative to the contours, preferably 45 to 135,generally the ridges only need to extend over a significant curvedregion of the contoured film.

The structured surfaces can be made by any known method of forming astructured film, such as the methods disclosed in U.S. Pat. Nos.5,069,404 and 5,133,516, both to Marantic et al.; U.S. Pat. No.5,691,846 to Benson et al.; U.S. Pat. No. 5,514,120 to Johnston et al.;U.S. Pat. No. 5,158,030 to Noreen et al.; U.S. Pat. No. 5,175,030 to Luet al.; U.S. Pat. No. 4,668,558 to Barber; U.S. Pat. No. 4,775,310 toFisher; U.S. Pat. No. 3,594,863 to Erb or U.S. Pat. No. 5,077,870 toMelbye et al. These methods are all incorporated by reference in theirentirety.

The contoured film layers are preferably provided with a high aspectratio structure over at least 50 percent of at least one face,preferably at least 90 percent. Cap film layers or other functional filmlayers can also be formed of these high aspect ratio structured films.Generally the overall flow channels should have structured surfacesforming 10 to 100 percent of its surface area, preferably 40 to 100percent.

The flow channel particulate filtration media of the present inventionstarts with the desired materials from which the layers are to beformed. Suitable sheets of these materials having the required thicknessor thicknesses are formed with the desired high aspect ratio surfacesand at least one of these film layers is contoured and this contouredfilm is stabilized by being joined to a further cap layer, a contouredlayer or the like, forming the flow channels. The flow channel layersforming the flow channel particulate filtration media, e.g., contouredfilm layers and cap layers, may be bonded together, mechanicallycontained or otherwise held into a stable flow channel particulatefiltration media. The contoured film and cap layers may be bondedtogether such as disclosed in U.S. Pat. No. 5,256,231 (extrusion bondinga film layer to a corrugated layer) or U.S. Pat. No. 5,256,231 (byadhesive or ultrasonic bonding of peaks to an underlying layer), or bymelt adhering the outer edges forming the inlet and/or outlet openings.As shown in FIG. 5 a contoured structured film 10 is joined to a planarstructured cap film layer 11 at the peaks 12 on one face 13 of thecontoured film layer 10. One or more of these flow channel layers 20 isthen stacked or otherwise layered and are oriented in a predeterminedpattern or relationship, with optionally additional layers 15 (FIG. 5A),to build up a suitable volume of flow channel layers 20 in a flowchannel particulate filtration media 30 as shown in FIG. 6. Theresulting volume of flow channel layers 20 is then converted, by slicingor otherwise, into a finished flow channel particulate filtration mediaof a desired thickness and shape. Any desired treatments, as describedabove, may be applied at any appropriate stage of the manufacturingprocess.

The flow channel particulate filtration media 30 is preferably formedinto its final form by slicing the array with a hot wire. The hot wirefuses the respective layers together as the final filter form is beingcut. This fusing of the layers is at the outermost face or faces of thefinal filter. As such at least some of the adjacent layers of the flowchannel particulate filtration media 30 need not be joined togetherprior to the hot wire cutting. The hot wire cutter speed can be adjustedto cause more or less melting or fusing of the respective layers. Forexample, the hot wire speed could be varied to create higher or lowerfused zones. Hot wires could be straight or curved to create filters ofan unlimited number potential shapes including rectangular, curved,oval, or the like. Also, hot wires could be used to fuse the respectivelayers of the flow channel particulate filtration media without cuttingor separating filters. For example, a hot wire could cut through theflow channel particulate filtration media fusing the layers togetherwhile maintaining the pieces on either side of the hot wire together.The pieces refuse together as they cool, creating a stable flow channelparticulate filtration media.

Preferred embodiments of the invention use thin flexible polymer filmshaving a thickness 9 of less than 200 microns, preferably less than 100microns down to about 5 microns. Thicker films are possible butgenerally increase pressure drop without any added benefit to filtrationperformance or mechanical stability. The thickness of the other layersare likewise preferably less than 200 microns, most preferably less than100 microns. The thickness of the layers forming the flow channelparticulate filtration media generally are such that cumulatively lessthan 50 percent of the cross sectional area of the flow channelparticulate filtration media at the inlet or outlet openings is formedby the layer materials, preferably less than 10 percent. The remainingportions of the cross sectional area form the inlet openings or outletopenings. The peaks or ridges of the contoured film generally have aminimum height of about 1 mm, preferably at least 1.2 mm and mostpreferably at least 1.5 mm. If the peaks or ridges are greater thanabout 10 mm the structures become unstable and efficiency is quite lowexcept for very long flow channel particulate filtration medias, e.g.greater than 100 cm or longer; preferably the peaks or ridges are 6 mmor less. The flow channels generally have an average cross sectionalarea along their length of at least about 1 mm² preferably at least 2mm² where preferably a minimum cross sectional area is at least 0.2 mm²,preferably at least 0.5 mm². The maximum cross sectional area isdetermined by the relative filtration efficiency required and isgenerally about 1 cm² or less, preferably about 0.5 mm² or less.

The shape of the flow channels is defined by the contours of thecontoured film layer and the overlying cap layer or adjacent attachedcontoured film layer. Generally the flow channel can be any suitableshape, such as bell shaped, triangular, rectangular or irregular inshape. The flow channels of a single flow channel layer are preferablysubstantially parallel and continuous across the contoured film layer.However, flow channels of this type on adjacent flow channel layers canbe at angles relative to each other. Also, these flow channels ofspecific flow channel layers can extend at angles relative to the inletopening face or outlet opening face of the flow channel particulatefiltration media.

The flow channel particulate filtration media is preferably from 8 to 35mm thick from the first face to the second face of the array. It hasbeen found that when the thickness is less than 8 mm, existing safetyregulations for motor vehicles may not be met. When the size exceeds 35mm, the combination filter may be too bulky to fit easily in the housingprovided therefor in the motor vehicle.

The flow channel particulate filtration media and the gas adsorbingfiltration media may be formed into the combination filter in any of theconventional ways. For example, the gas adsorbing filtration media maybe glued to the flow channel filtration medium by gluing the pleat tipsof the pleated gas adsorbing filtration media to the flow channelparticulate filtration media. Preferably however, the flow channelparticulate filtration media and the gas adsorbing filtration media willbe held together by a pair of strips along two opposing ends of thecombination filter. Such strips can be glued to the ends of the flowchannel particulate filtration media and the gas adsorbing filtrationmedia thereby holding both together in the combination filter. Suchstrips can be made of any material such as for example plastic and theycan be rigid as well as flexible or compressible. In accordance with aparticular embodiment, the strips can be flexible and compressible suchas, for example, a strip of foam or non-woven. The use of such a stripwill have the advantage that it could also function as a sealing againstthe housing in which the combination filter is to be fitted.

According to a particularly preferred embodiment, the flow channelfiltration medium and gas adsorbing filtration media will be heldtogether by providing a frame around the periphery of the combinationfilter. Such frame is preferably glued to the ends of the flow channelfiltration medium and the gas adsorbing filtration media. The frame canbe rigid and may be made of plastic or any other suitable material.Preferably, the frame is comprised of a flexible and compressiblematerial that can function as a frame as well as a sealing. Suchmaterials include for example foams and non-woven materials. Thanks tothe rigidity and stability of the flow channel particulate filtrationmedia, the frame does not need to be rigid and even a fairly flexiblematerial such as a foam can be used as the frame.

FIG. 12 shows a first embodiment of a combination filter. Thiscombination filter 200 includes a frame preferably comprised of frameportions 201 which are made of foam and which are glued to the lateralsides of a flow channel particulate filtration media 202 and a gasadsorbing filtration media 203. However, the frame can be made of anymaterial suitable as a filter holding frame. As can be seen from FIG.12, the gas adsorbing filtration media 203 comprises a pad 204 having alayer of constant thickness in the flow direction throughout its widthand length dimensions. The pad 204 comprises gas adsorbing particles 205adhered to each other by a suitable binder so that the pad 204 builds aporous layer. A layer of scrim 206 is arranged at that face of the pad204 facing away from the flow channel particulate filtration media 202.

As shown in FIG. 12, the flow channel particulate filtration media 202is made up of a stack of contoured film layers 207 and substantiallyflat layers 208 arranged alternatingly. These layers 207 and 208 areelectrostatically charged. At least one of the layers on at least one ofits sides is structured. Contoured film layers 207 and straight filmlayers 208 define flow channels 209 that extend from one face 210 of theflow channel particulate filtration media 202 to its opposite face 211.In use, face 210 will define the inlet and the layer of scrim 206 willdefine the outlet of the combination filter 200 with face 211 of theflow channel particulate filtration media 202 facing and contacting face212 of the pad 204 which face 212 is opposite to the layer of scrim 206of the gas adsorbing filtration media 203. Accordingly, the unfilteredfluid when flowing in flow direction 213 will enter at face 206 and movethrough the flow channel particulate filtration media 202 first and willthen flow through the pad 204 of the gas adsorbing filtration media 203.The pad 204 may comprise holes or channels (not shown) extending throughthe layer of the pad in flow direction 213. The number of holes orchannels per cm² is around 50 to 200 and in particular 100 with thediameter of the holes or channels about 0.5 to 2 mm and in particular 1mm.

FIG. 13 shows an alternative of a combination filter 300 which issimilar to the combination filter 200 of FIG. 12 and differs from thatcombination filter by the material of the pad 304 of the gas adsorbingfiltration media 303. In FIG. 13 the same reference numerals as in FIG.12 are used for the same parts but increased by 100.

In contrast to FIG. 12, the pad 304 of the combination filter 300 ofFIG. 13 comprises nonwoven web of fibers 305 which are entangled andloaded with gas adsorbing material (not shown) bonded to the fibers byfor example an adhesive or binder.

The following examples are intended to further illustrate the inventionwithout however the intention to limit the invention thereto.

EXAMPLES

The invention will be further described by the following examples andtest results:

Example 1

The flow channel particulate filtration media of a combination filterwas produced using the following method: Polypropylene resin was formedinto a structured film using standard extrusion techniques by extrudingthe resin onto a casting roll with a micro-grooved surface. Theresulting cast film had a first smooth major surface and a secondstructured major surface with longitudinally arranged continuousfeatures from the casting roll. The features-on the film consisted ofevenly spaced first primary structures and interlaced secondarystructures. The primary structures were spaced 150 microns apart and hada substantially rectangular cross-section that was about 75 microns talland about 80 microns wide (a height/width ratio of about 1) at the basewith a side wall draft of about 5°. Three secondary structures havingsubstantially rectangular cross-sections that were 25 microns tall and26 microns wide at the base (height/width ratio of about 1) were evenlyspaced between the primary structures at 26 micron intervals. The basefilm layer from which these features extended was 50 microns thick.

A first layer of structured film was corrugated into a contoured shapeand attached at its arcuate peaks to a second structured film to form aflow channel laminate layer assembly. The method generally comprisesforming the first structured film into a contoured sheet forming thefilm so that it has arcuate portions projecting in the same directionfrom spaced generally parallel anchor portions and bonding the spacedgenerally parallel anchor portions of the contoured film to a secondstructured film backing layer with the arcuate portions of the contouredfilm projecting from the backing layer. This method is performed byproviding first and second heated corrugated members or rollers eachhaving an axis and including a plurality of circumferentially spacedgenerally axially extending ridges around and defining its periphery,with the ridges having outer surfaces and defining spaces between theridges adapted to receive portions of the ridges of the othercorrugating member in mashing relationship. The first structured film isfed between the mashed ridges with the corrugating members arecounterrotated.

With the corrugating apparatus configured in this manner the structurefilm when passed through the inter-mashing teeth of the corrugatingmembers at a roll speed of 5.3 rpm was compressed into and retainedbetween the gear teeth of the upper corrugation member. With the firstfilm registered in the teeth of the upper corrugation member the secondstructured film was laid over the periphery of the roll and wasultrasonically welded to the layer retained in the teeth of the uppercorrugation member. Welding was accomplished between the first andsecond film at the top surface of the teeth of the corrugation member byemploying the tooth surface as an anvil against which an ultrasonic hornwas brought to bear. The thus formed corrugated flow channels were 1.8mm in height with a base width of 2.5 mm.

The flow channel layer assembly was electret charged by exposure to ahigh voltage field in a grid charger by the method generally describedin U.S. Pat. No. 3,998,916 (van Turnhout). A particulate filtrationmedia was formed from the charged flow channel layer assemblies bystacking layers on top of one another maintaining the channels in allthe flow channel layers in a parallel alignment such that the flowchannel walls formed a 90° angle with a plane defined by the inletopening phase of the flow channel particulate filtration media (90°incident angle). A filtration media array stack was converted into astable filtration media array construction by hot-wire cutting the stackto produce filters 10 mm in depth. The amount of melting induced by thehot wire and the degree of smearing of melted resin was carefullycontrolled so as not to obstruct the inlet or outlet openings of thefiltration media array. In addition to producing the desired filterdepth the hot-wire cutting process also stabilized the final assemblyinto a robust collapse resistant structure by fusing the front and rearphases of flow-channel layer assemblies together forming a stabilizedfiltration media array. For the combination filter system an array withthe external dimensions of 255×190 mm was created.

The second component of the combination filter, the gas adsorbingfiltration media was provided as a nonwoven layer of 255×190 mm widthand length dimensions and 12 mm thickness. The layer was comprised ofentangled fibers loaded with activated carbon adhered to the fibers. Theparameters of the gas adsorbing filtration media layer were as follows:

Weight [g/m²]: 2090 ± 12% Thickness [mm]: 12 Fibers: Weight [g/m²]:  420± 10% Share of the fibers 20 by mass [%]: Material of Fibers: Polyamide6.6 Adhesive: pressure sensitive adhesive RD-914 of Minnesota Mining andManufacturing Company Weight [g/m²]:  390 ± 20% Share of the adhesive 19by mass [%]: Activated Carbon: 25 × 45 meshes per inch, GG,Carbontetrachloride capacity (CTC) 80 Weight [g/m²]: 1280 ± 10% Share ofthe activated 61 carbon by mass [%]:

The flow channel particulate filtration media having a thickness of 10mm was placed onto the layer of gas adsorbing filtration media having athickness of 12 mm so that a configuration of a total thickness of 22 mmwas obtained. This configuration was then placed into a frame. For thisframe a closed cell polyurethane foam was used having a height of 22 mmand a thickness of 6 mm. On one side of the foam a double sided adhesivetape was applied with a liner which was subsequently removed. The foamwith the layer of adhesive material was then applied onto theconfiguration of the flow channel particulate filtration media and thegas adsorbing filtration media so that a frame was created. The framewas built up from four different pieces for each of the four sides,however, alternatively also a single strip of foam having the length ofthe entire circumference could also be used. With the application of thefoam and due to the rigidity of the flow channel particulate filtrationmedia a stable configuration was obtained without the two filtrationmedia being directly adhered to each other. Simultaneously this frame isalso capable of taking over the sealing function of the entirecombination filter.

Example 2

For this combination filter the same flow channel particulate filtrationmedia was used as in Example 1 and specified above.

For the gas adsorbing filtration media agglomerates were prepared, 110grams of treated activated carbon granules, 12×20 mesh (coconut derivedactivated GG carbon available from Kuraray in Okayama, Japan) wereheated at 165° C. for 45 minutes. The granules were treated with anaqueous solution of K₂CO₃ to improve the absorption of acid gas. Theseheated granules were then dry-mixed with 20 grams of polyurethane of aparticle size in the range of 50–225 microns (Morton PS 455-100,MORTON-THIOKOL, Seabrooke, N.H.) for 24 seconds in a mechanical mixer.The resultant carbon granule agglomerates adhered with binder particleswere sieved through a series of sieves with mesh sizes between 7–12. Thesieved agglomerates were then layered loosely in a mold with thedimensions 255×190 mm and heated at 165° C. for 40 minutes withoutcompression. This results in a thickness of 12 mm and an average densityof 0.25 grams per ccm. Further details of the method of preparation canbe taken from EP-B-0 652 803.

Example 3

For this combination filter the same flow channel particulate filtrationmedia and gas adsorbing filtration media of Example 2 were used exceptfor the porous layer of agglomerated carbon particles was provided withchannels extending in the flow direction. 400 of channels having adiameter of 1 mm were homogeneously distributed across the width andlength dimensions of the layer.

Comparative Example

The Comparative Example was a pleated construction using a conventionalelectret filter layer instead of the flow channel particulate filtrationmedia. A four layer laminate was created and subsequently pleated. As aparticulate filter the following was used: A scrim layer similar to theones used in Example 1 was used comprising a non-woven spun-bondedmaterial produced in a known manner from fibers being multiply thermallybonded and randomly arranged. The basis weight of this non-wovenspun-bonded material was 10 g/m². The spun-bonded web was combined witha non-woven material of the electret filter material consisting ofelectrostatically charged dielectric fibrillated or split fibers withthe typical dimensions of 10 by 40 microns in cross-section. The basisweight of this non-woven material was about 40 g/m². As materials forthis electret filter layer products distributed under the designation of3M Filtrete™ by the Minnesota, Mining and Manufacturing Company can beused.

The two other layers were practically identical to two layers of Example1 namely the adsorber particle layer as described above having athickness of 2 mm onto which a scrim layer was attached in the samemanner using an adhesive of the polyurethane group. The twoconfigurations namely the electret filter layer with the additionalscrim layer on one side and the adsorber particle layer with its scrimlayer on the other side were then laminated together so that theelectret filter layer was brought into direct contact with the adsorberparticle layer without using an adhesive. Accordingly, the two scrimlayers were at the two outer surfaces of the entire construction.

This configuration was then pleated in essentially the same manner asdescribed above creating a pleat height of 28 mm and an overalldimension of 255×190 mm resulting in a total of 20 pleats so that thetotal area of the active material was 0.21 m² comparable to the totalarea of Example 1 which was 0.22 m². The pleated configuration was thenplaced into a frame preferably through an injection molding process.

With the above described sample filters the following comparativemeasurements were conducted:

The efficiency was measured in accordance with the test norm DIN 71 460,part 1. The measurement of the efficiency is conducted as follows: Atest dust “coarse” according to DIN ISO 5011 is introduced according to§ 4.4 of DIN 71 460. This dust is measured with particle counters priorand after the entry through the filter to be tested. The particlecounters have the capability of determining particles of differentparticle sizes ranging between 0.5 and 15 microns at least. The ratiowithin this particle range then is the efficiency in percent. Allprovisions according to DIN 71 460, § 1-4.4.2, were taken into account.It is particularly important that the filters to be tested are identicalin size and configuration as stated above for the different examples.Furthermore, the captured dust was determined for Example 1 incomparison with the Comparative Example. Also in this case the testswere conducted following the test norm DIN 71 460 part 1. Thedetermination was conducted as follows: All provisions of DIN 71 460,part 1, were taken into account which are relevant for the determinationof the captured dust, especially § 6.3. The measurement was carried outfrom the beginning until the pressure drop had been increased at thegiven rates of 25, 50, 75 and 100 Pa respectively. The filters wereweighed prior and after the test. For the weighing also DIN ISO 5011 wasto be applied.

The gas efficiency was determined in accordance with the test norm DIN71 460, part 2. The filter to be tested is inserted into a test setupaccording to appendix A, figure A.1. In this case the test materialeither N-butane, SO₂ or toluene is introduced into the system in gaseousform. The temperature is determined and the concentration of the testmaterial is determined prior and after the passage through the filter.Simultaneously the pressure drop is measured. The concentration of thetest material prior to the entry into the filter is C₁, thecorresponding concentration after the passage through the filter is C₂.This is a function of the time, the test material is passing through thefilter (C₂ (t)) while the concentration prior to the entry of the testmaterial through the filter is constant with the time. The efficiency isthen determined byE _((t))=(1−C _(2(t)) : C ₁)*100%

As the filter is typically loaded up with the test material, theefficiency goes down with the time. For practical reasons it has beenproven that it is sufficient to indicate the different gas efficienciesimmediately after the test has started and the filter has begun toadsorb the test material (this means the gas efficiency after 0 minutes)and the gas efficiency after 5 minutes. Furthermore the flow rate has tobe taken into account which was 225 m³/h.

These tests were conducted with a number of samples in order to ensurethe reproducibility and the main results can be seen from the followingtable. This table gives a comparison between examples 1, 2, 3, and thecomparative example. From the table it can be seen that the pressuredrop increase over the amount of dust by which the combination filtersare loaded is much lower in case of examples 1, 2, and 3 than in case ofthe comparative example. That means that not only the dust collectioncapability of the combination filters of examples 1, 2, and 3 areimproved over the combination filter of the comparative example but alsothe life time is improved which is substantially longer for thecombination filter according to examples 1 to 3 than in case of thecomparative example.

The superior particle filtration performance of the flow channelparticulate filtration media of the combination filters of examples 1 to3 is maintained in the presence of the gas adsorbing filtration mediai.e. is not influenced by the layer of gas adsorbing filtration media.The performance of the gas adsorbing filtration media can be seen fromthe lower part of the table showing as an example the gas adsorbingperformance based on the gas efficiency for the test gas Toluene.

Comparative Example 1 Example 2 Example 3 Example particle filtrationperformance increase of 10 Pa   17 Pa 3 Pa      73 Pa pressure drop whenloaded with 20 g dust increase of 17 Pa >40 Pa 6 Pa >>125 Pa pressuredrop when loaded with 35 g dust gas adsorbing performance Toluene after69 78 63 83 0 min (initial) Toluene after 65 75 60 76 5 min (initial)

1. A combination filter for filtering fluids flowing in a flowdirection, comprising a flow channel particulate filtration media havinga first face and a second face and a gas adsorbing filtration media,wherein said flow channel particulate filtration media comprises aplurality of flow channels directed in a flow direction and defined byinner surfaces, said flow channels having inlet openings through thefirst face and outlet openings through the second face of said flowchannel particulate filtration media, wherein the inner surfaces of saidflow channels at least in part are provided with structures protrudingtherefrom and forming the flow channels or extending into the flowchannels or an electrical charge or a combination of both and whereinsaid gas adsorbing filtration media comprises a pad having a first faceand a second face and width and length dimensions orthogonal withrespect to each other and each individually to the flow direction andhaving a thickness dimension in the flow direction, said pad comprisinga layer extending substantially perpendicular to the flow directionacross the width and length dimensions of said pad.
 2. A combinationfilter according to claim 1, wherein said flow channel particulatefiltration media is formed by at least one structured film layer and asecond layer, the structured film layer having a first face and a secondface, at least one face of the structured film layer forming, at leastin part, said flow channels and having high aspect ratio structures overat least a portion of the face forming said flow channels and wherein asecond film layer comprising the flow channel layer, or a further layer,at least in part defines ordered fluid pathways through said flowchannel particulate filtration media and wherein said film layers definea plurality of inlets open through the first face and a plurality ofoutlets open through the second face of said flow channel particulatefiltration media.
 3. A combination filter according to claim 2 whereinat least one of the film layers in contoured to form said flow channels.4. A combination filter according to claim 1 wherein one of the faces ofsaid pad of said gas adsorbing filtration media is adjacent to thesecond face of said flow channel particulate filtration media.
 5. Acombination filter according to claim 1 wherein said pad of said gasadsorbing filtration media includes a porous structure of adsorberparticles connected to each other.
 6. A combination filter according toclaim 1 wherein the first and second faces of the pad of the gasadsorbing filtration media or the flow channel particulate filtrationmedia or of both the pad of the gas adsorbing filtration media and theflow channel particulate filtration media are parallel to each other. 7.A combination filter according to claim 1 wherein said pad of said gasadsorbing filtration media includes a nonwoven web of entangled fibersloaded with a gas adsorbing material.
 8. A combination filter accordingto claim 7 wherein the fibers have a diameter of from about 50 to 500microns.
 9. A combination filter according to claim 1 wherein said padcomprises holes or channels extending from the first face to the secondface of said pad.
 10. A combination filter according to claim 1 whereinsaid gas adsorbing filtration media further includes at least one scrimlayer arranged at one of the faces of said pad and wherein said flowchannel particulate filtration media and said gas adsorbing filtrationmedia are arranged such that said at least one scrim layer faces thefirst face of said flow channel particulate filtration media or isarranged so as to face away from the second face of said flow channelparticulate filtration media.
 11. A combination filter according toclaim 1 wherein said pad of said gas adsorbing filtration media has athickness of 5 to 30 mm.
 12. A combination filter according to claim 1wherein said flow channel particulate filtration media has a thicknessof 8 to 35 mm.
 13. A combination filter according to claim 1 furthercomprising at least two strips adhered at opposing edges of said gasadsorbing filtration media and said flow channel particulate filtrationmedia.
 14. A combination filter according to claim 13 wherein saidstrips comprise an adhesive tape.
 15. A combination filter according toclaim 13 wherein said strips comprise a foam.
 16. A combination filteraccording to claim 1 wherein said gas adsorbing filtration media andsaid flow channel particulate filtration media are surrounded by a frameat their periphery.
 17. A combination filter according to claim 1wherein the first face or second face or both faces of said gasadsorbing filtration media are corrugated.
 18. A combination filteraccording to claim 1 wherein said gas adsorbing filtration mediacomprise active carbon particles.
 19. Vehicle comprising a passengercabin and including a combination filter as defined in claim 1 forfiltering air entering into the passenger cabin.
 20. Method of filteringa fluid comprising causing said fluid to pass through a combinationfilter as defined in claim
 1. 21. Method according to claim 20 whereinsaid fluid is a gaseous fluid.
 22. Method according to claim 20 whereinsaid fluid is first passed through said flow channel filtration mediumand then through said gas adsorbing filtration media.